Transcript Current Climate Change: II

K38c: Current Climate Change–
Sea Level Rise
Thermal expansion, melt water,
salinity, geoid changes, Coriolis
contribution, and relation to
global temperatures
On ~60 year time scales, sea level rises for two
reasons, both are climate-related…
• 1. Thermal expansion of warmer water (simple physics. Observe
temperature profile of the ocean, integrate, derive the thermal
expansion)
• 2. Melting of continental “permanent” ice (glaciers, land ice caps)
• Thermal expansion has provided most of the sea level rise of the
past 100 years
• But continental melt is rapidly increasing, and now contributing
~1/2 of the current sea level rise rate, will dominate into future.
• Sea Level Rise rate = 1.8mm/year averaged over past 100 years, but
is 3.3mm/year over the past 20 years.
• Note that sea ice melting contributes nothing to sea level rise, since
floating ice already displaces water (Archimedes Principle). Thus,
melting of the Arctic Ocean ice is not contributing to sea level rise
• On longer time scales, there is minor contributions from slow rebound of
the land from the last Ice Age (loss of heavy glaciation causes
continental land to float a bit higher, and this process is very slow).
• On time scales of a few years and shorter, there are many factors
affecting sea level: tides, El Nino’s, tsunamis, changing atmospheric
pressure associated with storms, floods and associated salinity
changes…
• 34 second video of Greenland areas of ice melting (in red)
Observations (brown) are much higher than
predictions (blue). From IPCC AR4
The IPCC and Conservatism
• One more time – the Intergovernmental Panel on Climate Change,
though staffed in large part by high quality scientists, is a UN
organization and all parts of the organization must reach
UNANIMOUS agreement on everything they publish
• Given that the governments of the scientists are largely the most
carbon-polluting on Earth, and given the non-science people who
are part of that decision cohort, it’s not at all surprising that the
statements and writings of the IPCC are NOT “alarmist”, but in fact,
quite far on the “complacent” side of reality.
• Ocean scientist Jeremy Jackson points out (33 minutes into this
seminar) that as of IPCC AR5, there are enough assessment
reports to show that IPCC projections of sea level rise are less
than HALF of reality every single time.
• You should find this alarming, and put in context future IPCC
statements or quotes of their statements in the press
The Oceans Have Absorbed 93% of our
Greenhouse Heating
GISS Climate Model Post-diction Runs Agree
with Observed Ocean Heating. Rising Heat =
Expanding Volume and Rising Sea Level
Sea Level Rise vs.Time and Place
• El Nino’s tend to cause sharper rises in sea level where
the warm surface waters are, from the thermal
expansion of water
• La Nina’s (the (on average) cold surface water phase)
does the opposite and lowers local sea level
• The height of the geoid (the gravitational potential
energy surface of the Earth; a surface parallel to sea
level if all other factors are ignored) changes near
Greenland and Antarctica especially, as glacial melt
takes gravitational mass away from these continents
• Hence, the rate of sea level rise varies from place to
place at different times. Must take account of geoid
changes (straight-forward to do: gravity) and other data
sampled widely in location and time to get it right.
• The following data shows the many tidal gauges and
satellite measurements are doing a good job of tracking
global sea level rise
Latest Data, Seasonal Oscillation Removed. Note
intense La Nina in 2010/11 actually dropped sea
levels temporarily (rains moved water to land until
it could flow back to ocean)
New 2014 study by Hay et al. shows the
Pre-satellite (<1990) sea levels are biased
low, and sea levels were actually higher
• Therefore, 1900-1990 sea level rise rate now looks
to be a little lower than had been thought,
• This now agrees with satellite data.
Hay et al. 2014 is the higher brown curve. Shows
more obvious pause in 1950-1972, and stronger
acceleration since then
This indicates HIGHER acceleration
rate during the global warming era
than earlier data
• The lower rise rate in the 20th century
combined with the same high rate we see
today – means that the rise RATE of sea level
is accelerating faster than we had thought
• Recall we saw a similar bias in ocean
temperature due to faulty calibrations between
pre-WWII bucket-derived vs. newer hull and
then automated bouy ocean temperatures
How does this rise rate compare with Ice Age transitions? Red line is
1.8mm/yr = 20th century average. Recent rate (red line) is double that:
1993-2003 satellite observed rate is 3.3mm/yr
Antarctica and Greenland are Earth’s Ice Caps. GRACE
Satellite uses gravity to measure total ice mass loss from
Greenland. Ice loss is accelerating, raising sea levels
The 1950-70’s pause in global
temperature rise stabilized
Greenland ice. Now, in free-fall
Greenland Melt’s Contribution to Rate of Sea
Level Rise: Increasing At Accelerating Rate
Glacier Mass Loss Totals:
Accelerating Melt Worldwide
Annual change in global glacial melt contribution to sea level rise (left axis, mm
of water equivalent, mm/yr) and cumulative (brown dots, right axis), based on
surface area-weighted mass balance observations (source). Glacier melt now
provides almost as much sea level rise as does thermal expansion of seawater,
and will dominate going forward
Antarctic Ice Mass Declining Even Before WAIS
Collapse Began in 2014
Antarctica: Melt Rate Contribution to sea level rise rate
in mm/year. West Antarctic Ice Sheet (WAIS) is deep
red, left of the TransAntarctic Range
WAIS Pine
Island Glacier
terminus, lost
grounding in
2014. Collapse
of WAIS now
irreversible. Will
cause 10+ ft of
global sea level
rise over next
~century or so.
This 6min video
explains well
Why Are the West Antarctic Ice
Sheet Glaciers Melting Rapidly?
• Prime reason still calculated to be rising ocean temperatures,
according to Dr. Eric Rignot of who showed the ungrounding of the
terminus glaciers
• But, there is ongoing geothermal heating as well, since there is a rift
zone underneath the WAIS. However, there is no evidence that this
heat has taken a sudden rise rate in recent past, and the WAIS has
existed for 14-34 million years, even at its current below sea level
anchoring.
• Schroeder et al. 2013 finds the geothermal heat flow to be about
twice what had previously been estimated.
• Climate denialists are trumpeting this as destroying the credibility of
human-caused global warming (not!). Newer work by Fisher et al.
2015 (at UCSC) find this does NOT explain the rapid WAIS melting,
and that the WAIS developed with this geothermal heating already in
place. No evidence of recent increase in geothermal, but much
evidence of rapid recent rise in climate-induced ocean temps
surrounding Antarctica.
Key Points: Current Climate Change – Sea
Level
• 20th century average sea level rise rate: 1.7mm/year
• Past 20 years avg rate: 3.3 mm/year and rising fast
• Most sea level rise so far has been due to thermal expansion of
existing ocean water
• Most sea level rise in the future will be due to melting continental
ice, with help from thermal expansion
• Melting icebergs and other floating ice do NOT contribute to sea
level rise, by Archimedes Principle
• Glacier terminus in shallow coast ocean can be anchored by the
“grounding line”, slowing glacier flow, but thinning ice via warmer
water can unground the terminus, accelerating glacier slide into sea
• West Antarctic Ice Sheet now (2014) has begun irreversible
collapse, will cause ~10+ ft of sea level rise over next 1~2 centuries.
• A still minor contribution is geothermal heat from spreading zone
beneath WAIS, better measurements show ~twice what was earlier
thought, but not changing.